Low oxygen conditions (hypoxia) commonly found in solid tumors are considered a major obstacle for the clinical management of cancer by radiation therapy (radiotherapy, RT). Moreover, cancer patients with significantly hypoxic tumors tend to have a poor prognosis for survival. Given the clinical relevance of hypoxia, a long-time objective of experimental RT research has been to effectively radiosensitize solid tumors by attenuating or exploiting this pathophysiological state. Molecular oxygen (oxygen) is a natural and potent radiosensitizer; thus, one strategy for effectively treating hypoxic tumors by RT is to artificially increase their oxygenation. This project aims to use a novel oxygen-delivery technology developed at the University of California, Berkeley (UC Berkeley)-heme-nitric oxide/oxygen-binding (H-NOX) proteins-to revolutionize RT for cancer patients. The H-NOX technology embodies 4 major improvements over prior efforts in the field of oxygen delivery therapeutics: (1) oxygen-binding H-NOXs are neutral towards nitric oxide (NO), comparing favorably with the high NO reactivity and hypertensive properties of cell-free hemoglobin; (2) over 50 H-NOX candidates have been engineered, each with a specific oxygen affinity; the entire panel of vehicles demonstrate oxygen affinities across a 10-million fold range; (3) H-NOX vehicles are structurally stable above 75 oC, and chemically stable for weeks at room temperature; (4) H-NOX vehicles are modular, and can be surface-modified to alter size, oncotic properties, or tissue targeting. In short, the H-NOX technology provides a toolbox of oxygen delivery vehicles to test in hypoxic tissues and tumors for their capacity to raise oxygen levels and enhance RT and chemotherapy. To identify leading candidates for therapeutic development, select H-NOX candidates will be purified and applied to multilayered cell cultures (MCCs) exhibiting layers of hypoxia. Using sensitive quantitative microscopy, penetration of H-NOX into the tissue mass will be evaluated over time. Once the kinetics of tissue penetration are established, experiments will determine the alteration in tissue hypoxia as H-NOX vehicles penetrate and facilitate oxygen diffusion from the culture media to the hypoxic cell layers. Leading H-NOX candidates that demonstrate effective tissue penetration and reduction of hypoxia will be taken forward into animal studies. Mice carrying human tumor xenografts that exhibit significant hypoxia and resistance to RT will be treated with H-NOX vehicles and tumors will be evaluated for reduction in hypoxia compared to controls. Pharmacokinetic and toxicology studies will be performed in parallel to monitor the systemic effects of H-NOX administration. Should these experiments demonstrate reduction in tumor hypoxia, future experiments will evaluate enhanced RT tumor killing, and lead candidates will be promoted into development for testing in cancer patients carrying hypoxic tumors. [unreadable] [unreadable] PUBLIC HEALTH RELEVANCE: Low oxygen conditions (hypoxia) commonly found in solid tumors are considered a major obstacle for the clinical management of cancer by radiation therapy (radiotherapy, RT). For the 500,000 cancer patients treated with RT each year, more than 50% present with hypoxic tumors and respond poorly. This project aims to use a breakthrough, oxygen-delivery technology that is tunable, stable, and modular, to revolutionize RT for cancer patients. [unreadable] [unreadable] [unreadable]